The fabrication of microelectronics devices involves the deposition and removal of multiple layers of material on a semiconductor substrate to form active semiconductor devices and circuits. Device densities presently exceed 9 million transistors per square centimeter, and they are expected to increase by an order of magnitude within the next decade. Such devices utilize multiple layers of metal and dielectric materials that can selectively connect or isolate device elements within a layer and between layers. Integrated circuits using up to six levels of interconnects have been reported and even more complex circuits are expected in the future. Device geometries have gone from 0.5 micron to 0.12 micron and will soon be 0.08 micron. Multi-levels of metallization are required in such devices to achieve the desired speeds, and each inter-metal level must be planarized during the manufacturing process. A known process with the ability to create a sufficiently planar surface is chemical mechanical polishing (CMP). CMP may be used to remove high topography and/or to remove defects, scratches or embedded particles from the surface of a semiconductor wafer as part of the manufacturing process.
The CMP process generally involves rubbing a surface of a semiconductor wafer against a polishing pad under controlled pressure, temperature and rotational speed in the presence of a chemical slurry. An abrasive material is introduced between the wafer and the polishing pad, either as particles affixed to the polishing pad itself or in fluid suspension in the chemical slurry. The abrasive particles may be, for example, alumina or silica. The chemical slurry may contain selected chemicals, which function together with the abrasive to remove a portion of the surface of the wafer in a polishing action. The slurry also provides a temperature control function and serves to flush the polishing debris away from the wafer.
One important goal of CMP is achieving uniform planarity of the substrate surface. Uniform planarity includes the uniform removal of material from the surface of substrates as well as removing non-uniform layers that have been deposited on the substrate. Successful CMP also requires process repeatability from one substrate to the next. Thus, uniformity must be achieved not only for a single substrate, but also for a series of substrates processed in a batch.
One factor that contributes to non-uniform polishing is non-uniform distribution of the slurry at the interface of the substrate and the polishing pad. One known technique to alleviate the problem of poor slurry distribution has been to provide grooves in the pad. The grooves are believed to control the distribution of the slurry during operation by retaining a portion of the slurry in the grooves. However, while such pad designs accommodate more slurry volume than flat or planar pads, the pads have proved somewhat ineffective in achieving uniformity in slurry distribution because the inertia of the slurry causes the slurry to flow radially outward and off of the pad during rotation of the pad.
In an attempt to achieve uniform distribution of fresh slurry to all areas of the substrate, conventional techniques generally rely on supplying a relatively large volume of slurry to the pad during a polishing cycle. As a result, slurry becomes one primary consumable in chemical mechanical polishing and a significant source of the cost of operation. In order to reduce the cost of operation, the volume of slurry used in a processing cycle should be reduced. However, as noted above, conventional grooved pads generally are not capable of efficiently retaining the slurry between the pad and the substrate. As a result, the volume of consumed slurry is higher than is desirable.
Another issue, due to the presence of grooves on the polishing surface of a pad, can be mechanical effects that can affect the polishing characteristics of the pad. For example, the provision of grooves on the polishing surface can decrease the stiffness of the pad to an unacceptably low level, resulting in poor within-die uniformity.
Thus, it is desirable to provide a pad construction that would allow for an appropriate balance between rigidity (or stiffness) and compliance (or flexibility) of the polishing pad to ensure within-die uniformity. Moreover, it is desirable to provide a pad construction capable of reducing the cost of operation, such as by reducing the volume of slurry used in a processing cycle, as well as reducing a defect count, (e.g., number of scratches) that can develop over the surface of a wafer subjected to a CMP process.